Endocrine Abstracts

JOINT2423

Introduction: Advanced hyperthyroidism (HT) is characterized by high bone turnover, leading to osteoporosis. This disorder has rarely been reported in newly diagnosed hyperthyroid patients. This study aimed to determine the calcium-phosphate metabolism profile and bone mineral density (BMD) in patients with newly diagnosed HT.

Methods: A cross-sectional study was performed at the endocrinology department of Charles Nicolle Hospital in Tunis, Tunisia including newly diagnosed patients with HT from Juin to December 2023. We didn’t include pregnant, breast-feeding or menopausal women, subjects with co-morbidities (hyper or hypoparathyroidism, inflammatory bowel disease, malabsorptive disorder, renal disease, chronic liver disease, Cushing’s disease, hypogonadism) or having history of drug use (steroid, bisphosphonates, calcium or vitamin D). Biochimical markers of calcium-phosphate metabolism involving: corrected calcium, phosphate, parathyroid hormone (PTH) and 25-hydroxyvitamin D (25(OH)D) were assessed. BMD measurements were performed at the lumbar spine and the femoral neck.

Results: The study included 43 newly diagnosed hyperthyroid patients. The majority were female, comprising 31 individuals (72.1%). Mean age of participants was 39.1 ± 10.3 years. Graves’ disease was the most frequent etiology (90%) followed by toxic multinodular goiter. Mean levels of free thyroxine (FT4) and thyrotropin (TSH) were respectively 3.2 ± 1.8 ng/dl [NR: 0,7–1,8 ng/dl] and 0,03 ± 0,01 mUI/l [NR: 0,4 – 4 mUI/l]. Hypercalcemia (corrected calcium >2.5 mmol/l) and hyperphosphatemia (phosphate >1.45 mmol/l) were observed in 23.3% and 18.6% of patients, respectively. The majority of patients (60%) had a PTH level below 40 pg/ml, within the lower half of the normal range [NR: 15–60 pg/ml]. Twenty-nine patients (76.4%) had vitamin D insufficiency (25(OH)D <20ng/dl). Osteoporosis (T-score ≤ -2.5) and osteopenia (T-score between -2.5 and -1.0) were found in 14.7% and 26.5% of patients, respectively. The comparison between patients with and without osteoporosis showed significantly higher FT4 levels in patients with osteoporosis (P = 0.01). Receiver operating characteristic (ROC) analysis identified a significant FT4 cut-off value for predicting osteoporosis. The ROC-determined cut-off was 4,7 ng/dl (2.6 times the upper limit of normal) with a sensitivity of 60 % and a specificity of 93 % for predicting osteoporosis. Calcium, phosphate, PTH and 25 (OH)D were similar in the two groups of patients (P>0.05).

Conclusion: Our study showed that accelerated bone turn over occurs early in HT, causing an imbalance in calcium-phosphate metabolism. Reduced BMD correlates with disease severity. Osteoporosis should be assessed when FT4 levels exceed 2.6 times the upper limit of normal in newly diagnosed HT.